In several animal species, including man, activation of the adrenergic neurohumoral system evokes vascular responses as well as a rapid mobilization of lipids from adipose tissue. This suggests that the blood vessels, and possibly the adipocytes, are richly supplied with nerve fibers. In addition, there is evidence that the permeability of the vascular walls is altered by adrenergic activity. In dogs, stimulation of the nerves to subcutaneous adipose tissue produces an increased rate at which fluid moves through the microvascular walls. However, the exact anatomical relationship of nerves to blood vessels and adipocytes has not been determined. Furthermore, there is evidence that non-innervated adipocytes may receive adrenergic stimulation indirectly via cell-to-cell contact. The objectives of the proposed study are to (a) determine the anatomical distribution of nerves and nerve terminals in white adipose tissue, (b) describe the anatomical relationships between nerve terminals, microvessels and adipocytes and (c) determine the absence or presence of contacts between adipose cells. Adipose tissue from rats and mice will be isolated and perfused with 2% glutaraldehyde and 2% formaldehyde in 0.1 M cacodylate buffer. After fixation, the tissue will be excised and prepared for examination of the nerves with the light and electron microscope. In addition, cytochemical techniques will be used to identify catecholamines within nerves at the light and electron microscopic levels. In order to visualize the vascular bed, the vessels will be filled with a silicone elastomer to which a fluorescent dye has been added. Catalysts will be added to the base material for a timed polymerization. After the cast has hardened, the vascular bed in the tissue will be examined microscopically to determine the relationship between vessels, nerves and adipocytes. clarification of these relationships should enhance our knowledge of neurogenically evoked vascular responses as they relate to levels of plasma lipids. This may in turn contribute to a further understanding of atherosclerotic disease and its possible control.